1. Field of the Invention
The present invention relates to apparatus for controlling the tension of a web or strand being unwound from or wound into a ball or roll, and particularly for a creel for feeding out slivers of wool from a plurality of balls of sliver.
2. Description of the Prior Art
Creel mechanisms for concurrently unwinding a plurality of collections of material, such as ball tops of wool sliver to feed drawing machine or other utilization device, typically comprise a pair of generally parallel rollers, both coupled to a common drive mechanism so that they are rotated in the same direction at a substantially uniform speed. The rollers impart a rotational motion to the ball to unwind the material strand (e.g. sliver of wool) from the collection (e.g. ball) to feed the drawing machine. Typically, 10 to 24 wound balls of sliver are unwound by the same creel. However, since the balls are typically not of uniform density, unwinding the balls at the same speed, causes various of the balls to overfeed, often causing tangling and various others to underfeed often causing the strand to break, thus decreasing the efficiency of the operation.
In general, systems for controlling the tension of a web supplied from or to a storage reel are known. Examples, of such systems are described in U.S. Pat. Nos. 2,597,133 issued to F. D. Snyder on May 20, 1952 and 3,930,523 issued to M. Garcia on Jan. 6, 1976 and 4,146,190 issued to R. Bond et al on Mar. 27, 1979. For example, the Bond et al system utilizes two rollers driven in the same direction by a common sprocket and chain arrangement to wind a roll of material. Tension in the web is detected by a pivotally mounted spring biased dancer roll. The dancer roll is connected to a variable transformer, which effects a voltage variation in the power provided to and thus the torque provided by the drive motor of the device in accordance with the tension. Such systems are unduly complicated, and/or not readily adapted to accommodate concurrent feeding out of a plurality of balls.
Another example, of a take-up mechanism is described in U.S. Pat. No. 2,354,952 issued to L. Hornbostel on Aug. 1, 1944. The Hornbostel patent describes a paper winder which automatically maintains a desired drag on the material being wound to produce a uniformly hard roll of material. A pair of winding drums rotatably mounted in horizontally spaced relation receive a spool therebetween. One of the winder drums is directly driven by a prime mover, and serves to rotate the spool to roll a web of flexible material such as paper therearound. The other winder drum serves as a partial support for the spool and feeds the flexible material to the spool at a rate somewhat slower than the rate of rotation imparted by the first drum so that the paper will be tightly wound. A dynamic clutch or eddy current coupling is interposed between the slow drum and the driving mechanism so that the slow drum speeds up as the roll of paper being wound increases in size and weight, but never reaches the speed of the fast drum. The Hornbostel apparatus is unduly complicated and not readily adaptable for relatively light materials such as a ball top of wool, or for unwinding operations.
Another example of a tension control apparatus for winding rolls of web material is described in U.S. Pat. No. 1,720,118 issued July 9, 1929 to J. Corey. In the Corey apparatus a plurality of pairs of parallel rollers are provided, one pair associated with each roll of web. A separate drive motor is provided for each roller of each pair and the respective relative speeds of the individual rollers in each pair vary to control tension. Such an arrangement is unduly expensive.